Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
To:     rafael@kernel.org, lenb@kernel.org, hdegoede@redhat.com
Cc:     Kai-Heng Feng <kai.heng.feng@canonical.com>,
        linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v3] ACPI: video: Put ACPI video and its child devices to D0 at boot
Date:   Fri, 21 Jul 2023 23:21:43 +0800
Message-Id: <20230721152143.3108017-1-kai.heng.feng@canonical.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Screen brightness can only be changed once on HP ZBook Fury 16 G10.

Vendor identified the root cause as Linux doesn't invoke _PS0 at boot
for all ACPI devices:

    Scope (\_SB.PC00.GFX0)
    {
        Scope (DD1F)
        {
            Method (_PS0, 0, Serialized)  // _PS0: Power State 0
            {
                If (CondRefOf (\_SB.PC00.LPCB.EC0.SSBC))
                {
                    \_SB.PC00.LPCB.EC0.SSBC ()
                }
            }
	    ...
	}
	...
    }

The \_SB.PC00.GFX0.DD1F is the panel device, and its _PS0 needs to be
executed to make the brightness control work properly.

_PS0 doesn't get invoked for this device because _PSC is missing,
which violates ACPI spec 6.3, section 7.3.6. Commit 7cd8407d53ef
("ACPI / PM: Do not execute _PS0 for devices without _PSC during
initialization") tried to workaround missing _PSC on defective
firmwares, but got reverted because of regression.

So the safest approach is to use acpi_device_fix_up_power_extended() to
put ACPI video and its child devices to D0 to workaround the issue.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=217683
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
---
v3:
 - Wording change to make it clear it's a firmware issue.
 - Specify the device name in comment.

v2:
 - Wording
 - Bugzilla
 - Add comment

 drivers/acpi/acpi_video.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 62f4364e4460..1732780a672b 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -2027,6 +2027,12 @@ static int acpi_video_bus_add(struct acpi_device *device)
 	if (error)
 		goto err_put_video;
 
+	/*
+	 * HP ZBook Fury 16 G10 requires ACPI video's child devices have _PS0
+	 * evaluated to have functional panel brightness control.
+	 */
+	acpi_device_fix_up_power_extended(device);
+
 	pr_info("%s [%s] (multi-head: %s  rom: %s  post: %s)\n",
 	       ACPI_VIDEO_DEVICE_NAME, acpi_device_bid(device),
 	       video->flags.multihead ? "yes" : "no",
-- 
2.34.1